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air flow question

I have inherited a problem system that I could use some guidance. It is a 126000 gas furnace, I am installing to replace bad oil system, with 1800 cfm output. The previous contractor installed (2) a/c systems in home. One for 1ST and one for 2Nd, both 2 ton systems. Great right, WRONG. Second floor works great, 1ST floor uses duct work for furnace. Air handler is attached in center of duct run. Front of house doesn't get cool center somewhat, rear none. I would like to relocate coil to top of new furnace, put fan motor at low speed puts out 1225 cfm. Customer doesn't want to replace 2 year old system to install correct size. 1ST floor a/c also goes up 2ND floor supplies.

If I put dampers into supplies for second floor, do you think that this system has any chance of working? Customer has been advised,in writing, that any attempt to correct this issue short of system replacement will not be warrantied. I am looking at installing txv in system in an attempt to make work. Any suggestions would be greatly appreciated.

Lee Morano
3 Lees' Home Improvements.


  • Brad White_184
    Brad White_184 Member Posts: 135
    Tossing a coin

    On the cooling side, your having both as 2-ton systems at those airflows is like taking one tablespoon of hot cocoa mix in a quart of milk. You know it has some chocolate effect but the full flavor escapes you almost entirely.

    Those systems should be operating in the 650 to 850 CFM range each, 800 being a traditional ideal at 400 CFM per ton. You will not dehumidify with that tonnage/airflow combination unless you live in Arizona. Of course, you already know this...

    On the heating side, the 126 MBH beastie has a 64 degree rise as it is. I would not reduce the airflow below specifications anyway but that system especially has too far to go, by more than halfway downward.

    A TXV system solution has merit if the AC is over-sized compared to airflow, to my thinking. That is not the case here. If the cooling capacity is lost in all that air, I suspect it will always be seeking SST and never meter.

    I take it that cooling is the prime issue? I see no way to reconcile the H versus C requirements until you start with your own H and C calculations. In other words, the cooling capacity may be fine but the heating is way over-sized and the airflow with it. Or the heating is spot-on, so is the cooling (doubt it), but the delivery systems cannot be made to match.

    You may have to start from scratch at least on paper to prove things out one way or the other.

    Before you promise the Owner a "I will try but no guarantee" system, I would consider the calculated baseline and a strong inclination that what you are suggesting will not improve things perceptibly either. You may just be stirring the pot at their expense. You could spend a good deal of your time and their money and not see either of them again.

    I think if you can prove things out on paper, your argument for a system replacement will be supportable. They may still balk and have issues with the original installer, but that is cheaper than trying collect your due even if you are acting on good faith.

    I may be out on a limb here but that is my $0.02.

  • mtfallsmikey
    mtfallsmikey Member Posts: 765
    Situations like this

    Almost never have a happy ending, unless the system's faults are real obvious,simple, and easy to repair. I've been there, and you MAY get it right, but more than likely you will have a disgruntled customer and a hole in your wallet from your donation of parts and labor. Brad is right, show them how you can REALLY make this right, and if the customer doesn't bite...walk away. Crap installs make us all look bad, just a shame...but nothing new, it's been going on for time eternal...good luck!
  • lee_7
    lee_7 Member Posts: 458

    The heat is spot on. New furnace is now running and working awesome. Cooling is going to be upgraded to proper size and second floor unit will now be a backup for supplemental cooling on second floor, as we all know, the second floor is always warmer. Gave customer quote to relocate old system and adding zoning, Instead we have decided to do it right from the second time around. She will be much happier.

    On a side note on furnace, customer got a free duct cleaning when I turned on new system. Old williamson oil furnace with a belt driven blower to a 2000 cfm direct drive blower. The little flap on back of sofa blows like Old Glory in a hurricane. She loves it. Has never had so much heat in the 20 myears in house.
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